ByJulie Pace and Dan Sewell, Associated PressMarch 12, 2016

Republican presidential candidate Donald Trump smiles and prepares to give a thumbs-up to supporters ripping apart a sign that had read "No Place for Hate in Maine" during a Trump campaign rally in Portland, Maine, March 3.

VANDALIA, Ohio — Republican presidential candidates Marco Rubio and John Kasich suggested Saturday they may not support Donald Trump if he becomes the GOP nominee, as violence at the front-runner's rallies deepened the party's chaotic chasm.

Mr. Trump has denied that he has encouraged violence at his events. But the scenes from his aborted rally in Chicago on Friday night appeared to be a final straw for some rivals who had pledged to support the frontrunner at the first GOP debate, then reiterated that pledge as recently as March 3.

Senator Rubio (R) of Florida said Saturday it was "getting harder every day" to keep his word. Governor Kasich (R) of Ohio said the "toxic environment" Trump is creating "makes it very, extremely difficult" to support him.

The North Carolina [face punching] incident wasn’t isolated. Other Trump protesters have been roughed up and forcibly expelled. Reporters are targets too. According to an eyewitness account from a Washington Post reporter, on Tuesday Trump’s campaign manager Corey Lewandowski yanked another journalist out of Trump’s path by grabbing her arm, hard enough to leave bruises....

Yet Trump hasn’t forcibly condemned supporter violence. If anything he’s appeared to condone it. “I’d like to punch him in the face,” Trump said of one protester at a February rally. Asked at Thursday night’s GOP debate whether he’s to blame for the most recent rally assault, Trump said he hoped not. Then he said in essence that the protesters deserve it.

“We have some protesters who are bad dudes, they have done bad things.... They’ve got to be taken out, to be honest,” Trump said....

The real estate billionaire is also pushing a strong-arm approach on policy. Perhaps that helps the rowdy atmosphere develop. He’s not just opposed to illegal immigration – he’s going to shut it off entirely with a wall that will be free because Mexico will pay for it. The US will seize Middle East oil to pay for its military operations in the region. Other countries are “laughing at our stupidity” on trade, and he’ll make them cry instead.

[Dr. Carson's] official statement did not refer to any other candidate by name, but nonetheless included some gentle barbs apparently directed at the brash Republican front-runner, businessman Donald Trump.

"I hope my presence added a measure of civility to the race," he said. "Many today are making decisions based on fear and anger."

He declined to endorse any of his competitors, but urged his fellow Republicans to choose based on "how they treat their family and others ... how they collaborate with others ... their ethics, because what America needs is 'Trickle-down ethics.' "

President Barack Obama, speaking at a Democratic fundraiser in Dallas, said those who aspire to lead the country "should be trying to bring us together and not turning us against one another." He said leaders should also "speak out against violence."

He did several interviews as cable networks broadcast footage of the skirmishes both inside and outside the Chicago arena where he had planned to speak.

Tensions ran high at Trump's latest rally, when US Secret Service agents briefly formed a protective ring around the presidential candidate, then left the stage and allowed him to continue speaking at an airport hangar outside Dayton, Ohio.

Trump's campaign said the agents rushed the stage after a man attempted to breach the security buffer. The man was "removed rapidly and professionally," spokeswoman Hope Hicks said.

As the agents rushed the stage, the audience chanted Trump's name. The candidate did not explain what had happened, but said: "Thank you for the warning. I was ready for 'em, but it's much better if the cops do it, don't we agree?"

Trump also had stops scheduled Saturday in Cleveland, Ohio, and Kansas City, Missouri.

The brash billionaire's unexpected political success has roiled the Republican Party. Most leaders expected his populist appeal would fade as voting contests began and largely avoided criticizing even his most extreme comments out of fear of alienating his supporters.

But after 24 primary elections and caucuses, Trump remains the front-runner and leads his rivals in the all-important delegate count.

GOP leaders are grasping for a last-ditch idea to stop Trump from claiming the nomination. They've talked about a contested convention and about whether to rally around a yet-to-be-determined third-party candidate. All are long shots at best and would probably rip the Republican Party apart.

Rubio and Kasich must win their winner-take-all home state contests Tuesday to stay in the race. Texas Sen. Ted Cruz, closest to Trump in the delegate count, has urged both to drop out so he can take on the front-runner in a head-to-head contest.

Cruz said late Friday that Trump has created "an environment that encourages this sort of nasty discourse."

"When the candidate urges supporters to engage in physical violence, to punch people in the face, the predictable consequence of that is that it escalates," he said.

As Mr. Grier wrote:

Trump’s candidacy for president attracts people who are angry enough to threaten others. That may be because Trump himself is unpredictable and prone to aggressive outbursts. Yet the United States system of government is based on a complicated system of balances and shared authority. Different groups have to cooperate to make it run. In America, you can’t punch your way to power.

The chaos in Chicago was sparked in part by Trump's decision to cancel his rally after skirmishes broke out in the crowd that, unlike past Trump events, was packed with protesters — many of whom had organized ahead of time with the intent of keeping Trump from speaking.

Many anti-Trump attendees had rushed onto the floor of the University of Illinois at Chicago Pavilion, jumping up and down with their arms up in the air after the event was called off. Some isolated confrontations took place afterward and police reported arresting five people.

As Trump attempts to unify a fractured Republican Party before Tuesday's slate of winner-take-all primary elections, the confrontations between his legion of loyal supporters and protesters who accuse him of stoking racial hatred have become increasingly contentious, underscoring concerns about the divisive nature of his candidacy.

In a telephone interview after postponing his event in Chicago, Trump said he didn't "want to see people hurt or worse" at the rally, telling MSNBC, "I think we did the right thing."

But Chicago police said they had sufficient manpower on scene to handle the situation and did not recommended Trump cancel the rally. That decision was made "independently" by the campaign, said police spokesman Anthony Guglielmi.

Trump’s candidacy for president attracts people who are angry enough to threaten others. That may be because Trump himself is unpredictable and prone to aggressive outbursts. Yet the United States system of government is based on a complicated system of balances and shared authority. Different groups have to cooperate to make it run. In America, you can’t punch your way to power.